F.1131 on a Viessmann One Base: Network fault (LAN)
Short answer
On a Viessmann heat pump, F.1131 means: Network fault (LAN). The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Network fault (LAN).
Part involved: Network fault (LAN).
When it shows: System characteristics:; Limited function of Energy Management (EMS); Inverter protects connected components by controlling the current feed (secure operation).
Likely causes:
- Network fault (LAN) No connection between Energy Management (EMS) and external photovoltaic gateway, e.g. Solar-Log Base gateway.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Not stated per code in Viessmann document 6199893 GB 01/2026 (VSA00009).
Manual reset: User may acknowledge via HMI after noting the code (6249162 p.57); the message returns if the cause persists.
What you can check
- On the HMI, tap the message and "?" to read the system characteristics and Viessmann's user tips; note the code (e.g. F.xxx) and text for your contractor (operating instructions 6249162 p.57).
- Acknowledge the message once via the HMI; do not acknowledge fault messages several times in quick succession (6249162 p.58) - notify your contractor.
- Check the heat pump breaker/isolator in the consumer unit is ON (do not repeatedly reset a breaker or RCD that keeps tripping).
- Check your home router/internet connection is working.
What the engineer will check
- Check messages from Energy Management (EMS) via ViGuide.
- Check LAN cable and plug-in connection between Energy Management (EMS) and external photovoltaic gateway:.
- Check wires and plugs for correct seating.
- Check connections for contact corrosion.
- Check cables for mechanical damage, e.g. crushing, kinking, chafing or breakage.
- Check network configuration for Energy Management (EMS) via ViGuide.
- Check network configuration via web interface of external photovoltaic gateway.
- Inform the manufacturer's technical support.
Who to ask for: Viessmann-trained heat pump engineer / qualified electrician.
Certification: Qualified electrician for work on electrical equipment (Viessmann safety instructions).
Sources
- Service instructions for contractors: Heat pumps in monoblock design incl. hybrid – System configuration and diagnostics (Vitocal 150-A/151-A/250-A/252-A, IDU-A, AWMOF-151/251, AquaSnap 30AWH, BI-BLOC R290) (6199893 GB 01/2026) ↗ · 6199893 GB 01/2026 (VSA00009) · page 185-186 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026